Ion beam etching method and ion beam etching apparatus

ABSTRACT

An ion beam etching method comprises an etching step of etching an object to be processed with an ion beam extracted by an extraction electrode, and a cooling step of cooling the extraction electrode with an inert gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ion beam etching method and an ion beam etching apparatus.

2. Related Background Art

An ion beam etching method has been known, which irradiates a surface of an object to be processed with an ion beam, so as to etch the object (see, for example, Japanese Translated International Publication No. 2002-510428). Such an ion beam is obtained when ions in a plasma generated in a discharge container in an ion source are extracted by an extraction electrode.

SUMMARY OF THE INVENTION

When a voltage is applied to the extraction electrode in order to extract the ion beam, however, the extraction electrode may be deformed by the heat of the plasma generated in the discharge container. When an extraction electrode made of three metal plates is used, for example, respective heat quantities supplied to the metal plates from the plasma differ from each other, whereby the metal plates deform by respective amounts different from each other. Therefore, respective center positions of extraction holes formed in the metal plates may deviate from each other. Extracting the ion beam with such an extraction electrode may be problematic in that (1), since the ion beam fails to have a fixed emission direction, the ion beam intensity exhibits an uneven radial distribution; (2) the ion beam extraction efficiency decreases; and so forth.

Therefore, it is an object of the present invention to provide an ion beam etching method and an ion beam etching apparatus which can restrain the extraction electrode from being deformed by heat.

For achieving the above-mentioned object, the ion beam etching method of the present invention comprises an etching step of etching an object to be processed with an ion beam extracted by an extraction electrode, and a cooling step of cooling the extraction electrode with an inert gas. The cooling step may be performed either after or before the etching step.

Preferably, the object is conveyed in the cooling step. The conveyance of the object may be started before the cooling step or continued after the cooling step.

Preferably, the cooling step is performed prior to the etching step, whereas the ion beam etching method further comprises a warming-up step of extracting the ion beam by using the extraction electrode prior to the cooling step.

Preferably, the inert gas is identical to an ion-generating gas for generating an ion in the ion beam in the etching step.

Preferably, the inert gas has a flow rate greater than that of the ion-generating gas in the cooling step.

The ion beam etching apparatus comprises an ion source, an extraction electrode for extracting an ion beam from the ion source, and a cooling device for cooling the extraction electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the structure of the ion beam etching apparatus in accordance with an embodiment;

FIG. 2 is a view schematically showing a main part of the ion beam etching apparatus shown in FIG. 1;

FIG. 3 is a flowchart showing a procedure for carrying out the ion beam etching method in accordance with an embodiment;

FIG. 4 is a flowchart showing the procedure for carrying out the ion beam etching method in accordance with the embodiment;

FIG. 5 is a flowchart showing the procedure for carrying out the ion beam etching method in accordance with the embodiment; and

FIG. 6 is a graph schematically showing the relationship between the value of RF power supplied from a power supply to a coil and time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. In the explanation of the drawings, constituents identical or equivalent to each other will be referred with numerals identical to each other without repeating their overlapping descriptions.

FIG. 1 is a diagram schematically showing the structure of the ion beam etching apparatus (also referred to as ion milling apparatus) in accordance with an embodiment. FIG. 2 is a view schematically showing the structure of a main part of the ion beam etching apparatus shown in FIG. 1.

The ion beam etching apparatus 100 shown in FIG. 1 is favorably used for manufacturing a thin-film magnetic head (e.g., GMR head or TMR head) for HDD. It is favorably used for processing an ABS defining the flying height of the thin-film magnetic head or chamfer part in particular. The ion beam etching apparatus 100 comprises an ion source 40, and an extraction electrode E for extracting an ion beam IB from the ion source 40. The ion beam IB advances through an etching chamber 30, so as to etch a substrate W (object to be processed) accommodated in the etching chamber 30. The extraction electrode E is constructed by molybdenum (Mo), for example, and is arranged between the etching chamber 30 and ion source 40. The substrate W is a silicon wafer, for example. The ion beam IB includes cations such as Ar⁺. However, the ion beam IB is not restricted to cations.

A neutralizer 34 for neutralizing the ion beam IB is placed within the etching chamber 30. When the ion beam IB is made of cations such as Ar⁺, for example, the neutralizer 34 emits electrons e⁻. The electrons e⁻ allow the space within the etching chamber 30 to be filled with positive charges, and can restrain the substrate W from being charged, for example. This can improve the extraction efficiency of the ion beam IB and restrain the ion beam IB from radially diverging.

A shutter 32 which can block the ion beam IB as necessary is placed within the etching chamber 30. The shutter 32 is arranged between the substrate W and extraction electrode E. For example, a mechanical shutter or electrostatic shutter can be used as the shutter 32. Further, a tray holder 36 for holding the substrate W at a predetermined position is placed within the etching chamber 30. Preferably, the tray holder 36 is cooled with a coolant cooled by a chiller (not depicted).

In this embodiment, a transfer chamber 20 is connected to the etching chamber 30 through a joint 52. A load-lock chamber 10 is connected to the transfer chamber 20 through a joint 50. The substrate W is introduced from the load-lock chamber 10 into the etching chamber 30 by way of the transfer chamber 20.

A rotary pump RB and a turbomolecular pump TP, for example, are connected to each of the load-lock chamber 10, transfer chamber 20, and etching chamber 30. A dry pump may be used in place of the rotary pump RP. The rotary pump RP and turbomolecular pump TP and the like keep a predetermined pressure (e.g., 0.05 Pa) within the etching chamber 30.

A robot arm 24 attached to a rotary shaft 22, for example, is arranged within the transfer chamber 20. A leading end of the robot arm 24 can hold a tray 26 for accommodating the substrate W. Preferably, the tray 26 is provided with a clamp part which is not depicted. The clamp part secures the substrate W to the tray 26. A plurality of substrates W may be accommodated in the tray 26 as well. The robot arm 24 can freely expand and contract longitudinally. Therefore, the robot art 24 can convey the tray 26 set within the load-lock chamber 10 into the etching chamber 30.

The ion source 40 comprises a discharge container 42 and a coil 44, provided on the outside of the discharge container 42, for generating a plasma P within the discharge container 42. Preferably, the discharge container 42 is made of a material mainly composed of a dielectric material such as quartz or an oxide of aluminum, for example.

A power supply 48 is connected to one end of the coil 44 through an impedance-matching device 46, for example. The other end of the coil 44 is grounded, for example. The power supply 48 is a high-frequency power source or high-frequency amplifier. In this case, the frequency of the power supply 48 is preferably several megahertz to ten-odd megahertz (e.g., 2 to 13.5 MHz). In one example, the frequency of the power supply 48 is 4 MHz, for instance. Preferably, the power supply 48 applies a power of 200 to 2,000 W, for example, to the coil 44 depending on the volume and form of the discharge container 42.

The discharge container 42 is formed with an opening 43 for introducing an inert gas, for example. One end of a pipe P1 is connected to the opening 43. The other end of the pipe P1 is connected to a gas supply source G1 through a gas box GB. The gas supply source G1 feeds an inert gas into the discharge container 42. Rare gases such as Ar gas and He gas, for example, can favorably be used as the inert gas. He gas is preferably used from the viewpoint of thermal conductivity. Ar gas is preferably used from the viewpoint of cost. The gas box GB has a valve V1, a mass flow controller MFC1, and a valve V2 successively from the upstream side. The mass flow controller MFC1 can regulate the flow rate of the inert gas fed into the discharge container 42.

Preferably, the inert gas fed from the gas supply source G1 is an ion-generating gas for generating the plasma P within the discharge container 42 while being a cooling gas for cooling the extraction electrode E. This can easily cool the extraction electrode E. Alternatively, the inert gas fed from the gas supply source G1 may be a cooling gas, while an inert gas fed from a gas supply source different from the gas supply source G1 may be an ion-generating gas.

The tray holder 36 is formed with an opening 33 for supplying a substrate-cooling gas for cooling the substrate W, for example. Preferably, the opening 33 is formed in the front face 36 a of the tray holder 36. When the direction (angle) of opening 33 is tilted, the opening 33 can be formed in a side face of the tray holder 36. A rare gas such as He gas can favorably be used as such a substrate-cooling gas. One end of a pipe P2 is connected to the opening 33. The other end of the pipe P2 is connected to a gas supply source G2 through the gas box GB. The gas box GB has a valve V3, a mass flow controller MFC2, and a valve V4 successively from the upstream side. The mass flow controller MFC2 can regulate the flow rate of the substrate-cooling gas. The substrate-cooling gas can restrain the substrate W from increasing its temperature during etching.

Specifically, the substrate-cooling gas blows the tray 26, so as to cool the substrate W by way of the tray 26, for example. The tray holder 36 and tray 26 may have such a structure that the substrate-cooling gas directly blows the substrate W. Examples of such a structure include a structure in which the bottom face part of the tray 26 is formed with a hole to become a gas flow path, and a structure in which the surface 36 a of the tray holder 36 is substantially annular so as to surround the tray 26 while the substrate-cooling gas is fed from the surface 36 a toward the center of the tray 26.

Preferably, the extraction electrode E has a screen grid E1, an acceleration grid E2, and a deceleration grid E3. The extraction electrode E may be free of the deceleration grid E3. The screen grid E1, acceleration grid E2, and deceleration grid E3 are arranged successively from the inside to outside of the discharge container 42. Each of the screen grid E1, acceleration grid E2, and deceleration grid E3 is a metal plate formed with a plurality of (e.g., 10,000 or less) extraction holes, for example. Preferably, the center positions of the extraction holes in the screen grid E1, the center positions of the extraction holes in the acceleration grid E2, and the center positions of the extraction holes in the deceleration grid E3 are designed so as to align with each other as seen in the thickness direction of the metal plates.

The screen grid E1 can separate the plasma P and the acceleration grid E2 from each other. For example, a power source 60 for continuously applying a positive high voltage is connected to the screen grid E1. The voltage applied to the screen grid E1 is 2 kV, for example. The voltage applied to the screen grid E1 determines the ion beam energy of the ion beam IB.

The acceleration grid E2 is also known as suppression electrode. For example, a power source 62 for continuously applying a negative high voltage is connected to the acceleration grid E2. The voltage applied to the acceleration grid E2 is −600 to −800 V, for example. The deceleration grid E3, which is also known as earth electrode, is grounded. When the potential difference between the acceleration grid E2 and deceleration grid E3 is adjusted, the ion beam diameter of the ion beam IB can be regulated so as to fall within a predetermined numeric range by using a lens effect.

The ion beam IB is emitted from the ion source 40 as follows, for example. First, the inside of the discharge container 42 is vacuumed to a pressure of about 10⁻⁵ Pa, for example, and an inert gas such as Ar gas is introduced from the gas supply source G1 into the discharge container 42. Subsequently, the power supply 48 feeds power to the coil 44, so as to generate a plasma P within the discharge container 42. Ions such as Ar⁺ in the plasma P are extracted as the ion beam IB by the extraction electrode E.

Here, the ions such as Ar⁺ in the plasma P impinge on the extraction electrode E, thereby raising the temperature of the extraction electrode E. The extraction electrode E also raises its temperature when a voltage is applied thereto. Therefore, etching raises the temperature of the extraction electrode E.

However, the ion beam etching apparatus 100 can cool the extraction electrode E by using the inert gas fed from the gas supply source G1 and gas box GB (cooling device). Cooling the extraction electrode E can restrain it from raising the temperature. As a result, thermal deformation can be suppressed in the extraction electrode E. This can suppress relative positional deviations among centers of the respective extraction holes in the screen grid E1, acceleration grid E2, and deceleration grid E3 within a predetermined range. Therefore, the radial distribution of ion beam intensity can be homogenized, while the extraction efficiency of the ion beam IB can be improved. Here, units such as tray holder 36 may be cooled simultaneously with the extraction electrode E.

When the radial distribution of ion beam intensity is homogenized, the in-plane distribution of etching amount (etching depth) in the substrate W can be homogenized, which enables etching with a high precision and excellent reproducibility. On the other hand, an improvement in the extraction efficiency of the ion beam IB can shorten the etching time and reduce the temporal fluctuation in the value of power fed from the power supply 48 to the coil 44.

FIGS. 3 to 5 are flowcharts showing a procedure for carrying out the ion beam etching method in accordance with an embodiment. FIG. 4 is a flowchart subsequent to FIG. 3. FIG. 5 is a flowchart subsequent to FIG. 4. The ion beam etching method in accordance with this embodiment is favorably carried out by using the above-mentioned ion beam etching apparatus 100.

The ion beam etching method in accordance with this embodiment will now be explained with reference to FIGS. 1 to 5. The ion beam etching method in accordance with this embodiment comprises a cooling step S52 of cooling the extraction electrode E with the inert gas, and an etching step S54 of etching the substrate W with the ion beam IB extracted by the extraction electrode E (see FIG. 4).

This embodiment carries out the etching step S54 after the cooling step S52. Preferably, a warming-up step S50 of extracting the ion beam IB by using the extraction electrode E is carried out prior to the cooling step S52 (see FIG. 3). The warming-up step S50 can determine whether the desirable ion beam IB is obtained or not. The warming-up step S50 may be omitted.

More specifically, the ion beam etching method in accordance with this embodiment is carried out favorably when the following steps S1 to S29 are effected in succession. In the following, a case where Ar gas is used as the inert gas fed to the discharge container 42 will be explained by way of example. In this case, Ar gas functions as an ion-generating gas for generating a plasma P within the discharge container 42 and as a cooling gas for cooling the extraction electrode E.

At step S1, the tray accommodating the substrate W is put into the load-lock chamber 10. Here, the load-lock chamber 10 is in its vented state (open to the air). On the other hand, pressures within the transfer chamber 20 and etching chamber 30 are set to their respective predetermined degrees of vacuum.

At step S2, the load-lock chamber 10 is vacuumed by using the rotary pump RP and turbomolecular pump TP. Preferably, rough vacuuming by the rotary pump RP is initially effected, and then is switched to vacuuming by the turbomolecular pump TP at the point where the pressure within the load-lock chamber 10 is several Pa. This allows the load-lock chamber 10 to attain high vacuum (e.g., 1×10⁻⁵ to 1×10⁻⁴ Pa) therewithin.

At step S3, it is determined whether or not a predetermined degree of vacuum at which the tray 26 can be conveyed has been achieved within the load-lock chamber 10. When it is determined that the predetermined degree of vacuum has been achieved as a result, a predetermined flow rate of Ar gas is introduced from the gas supply source G1 into the discharge container 42 at step S4. The flow rate of Ar gas is controlled by the gas box GB. Here, it will be preferred if the neutralizer 34 emits the electrons e⁻ within the etching chamber 30. When it is determined that the predetermined degree of vacuum has not been achieved, the flow returns to step S2, so as to vacuum the load-lock chamber 10.

After step S4, the warming-up step S50 is carried out. Preferably, the warming-up step S50 includes steps S5, S6, and S7. At step S5, the power supply 48 feeds RF power to the coil 44. This generates a plasma P including active species such as Ar⁺, electrons, and neutral Ar atoms. Preferably, the value of RF power is gradually increased here. As the active species impinge on, the discharge container 42 and extraction electrode E are heated, while the inner face of the discharge container 42 is cleaned. In particular, the screening grid E1 raises the temperature more than the acceleration grid E2 and deceleration grid E3 do.

At step S6, a voltage is applied to the extraction electrode E by using the power sources 60, 62. This causes the extraction electrode E to emit the ion beam IB. Here, the shutter 32 is in its closed state, whereby the ion beam IB is blocked by the shutter 32.

At step S7, it is determined whether or not the warming up for the ion beam IB is completed. When it is determined that the warming up is completed, the power applied to the extraction electrode E is turned OFF at step S8. The irradiation time of the ion beam IB is about 5 minutes, for example. When the warming up is completed, the irradiation with the ion beam IB becomes stable. When it is determined that the warming up is not completed, the flow returns to step S5, so as to keep feeding the coil 44 with the RF power.

At step S9, the RF power supplied to the coil 44 is turned OFF. This stops the irradiation with the ion beam IB. Thereafter, the neutralizer 34 stops emitting the electrons e⁻. At step S10, the shutter 32 is opened.

After step S10, the cooling step S52 is carried out. Preferably, the cooling step S52 includes steps S11, S12, and S13. At step S11, the flow rate of Ar gas fed from the gas supply source G1 into the discharge container 42 is preferably greater than the flow rate of Ar gas at step S4, more preferably maximized (e.g., to 300 sccm). Here, it will be preferred if the pressure within the etching chamber 30 is at least 100 times that at the time of warming up. The flow rate of Ar gas is controlled by the gas box GB.

At step S12, the tray 26 is conveyed. The tray 26 is conveyed by the robot arm 24 from within the load-lock chamber 10 to an origin position on the front face 36 a of the tray holder 36 within the etching chamber 30, and is fixed at the origin position. The substrate W is conveyed together with the tray 26.

At step S13, the tray holder 36 is rotated and tilted, so as to set the tray 26 at a predetermined position. This adjusts the angle of incidence of the ion beam IB with respect to the substrate W.

At step S14, the feeding with Ar gas is stopped. At step S15, the etching chamber 30 is vacuumed. At step S16, it is determined whether or not a predetermined degree of vacuum is attained. When it is determined that the predetermined degree of vacuum is attained as a result, a predetermined flow rate of Ar gas is introduced from the gas supply source G1 into the discharge container 42 at step S17 as with step S4. When it is determined that the predetermined degree of vacuum is not achieved, by contrast, the flow returns to step S15, so as to vacuum the etching chamber 30. Here, it will be preferred if the neutralizer 34 emits electrons e⁻¹ within the etching chamber 30. Since the etching chamber 30 and the discharge container 42 are connected to each other through the holes of the extraction electrode E, vacuuming the etching chamber 30 makes the inside of the discharge container 42 attain a degree of vacuum on a par with that within the etching chamber 30.

After step S17, the etching step S54 is carried out. Preferably, the etching step S54 includes steps S18, S19, and S20. At step S18, the power supply 48 feeds the coil 44 with RF power as with step S5. This generates a plasma P within the discharge container 42. Preferably, the value of RF power is gradually increased here. The plasma P heats the discharge container 42 and extraction electrode E. Preferably, in order to prevent the temperature of the substrate W from rising during etching, He gas which has been heat-exchanged with the coolant cooled by the chiller is caused flow between the substrate W and the tray 26. At step S19, a voltage is applied to the extraction electrode E by using the power sources 60, 62 as with step S6. This allows the extraction electrode E to emit the ion beam IB, so that the ion beam IB impinges on the substrate W, thereby starting etching.

At step S20, it is determined whether or not a predetermined etching time has elapsed. When it is determined that the predetermined etching time has elapsed as a result, the voltage applied to the extraction electrode E is turned OFF. When it is determined that the predetermined etching time has not elapsed, by contrast, the flow returns to step S18, so as to keep feeding the coil 44 with the RF power.

At step S22, the RF power fed to the coil 44 is turned OFF. This stops the irradiation with the ion beam IB. Thereafter, the neutralizer 34 stops emitting the electrons e⁻.

At step S23, the supply of Ar gas is stopped. At step S24, the shutter 32 is closed. At step 25, the tray holder 36 is rotated and tilted, so as to return the tray 26 to the origin position. At step S26, the tray 26 is conveyed. The tray 26 is conveyed from the origin position on the front face 36 a of the tray holder 36 into the load-lock chamber 10 by the robot arm 24.

At step S27, the load-lock chamber 10 is vented. At step S28, it is determined whether or not the venting is completed. When it is determined that the venting is completed as a result, the tray 26 is taken out from the load-lock chamber 10. When it is determined that the venting is not completed, by contrast, the flow returns to step S27, so as to vent the load-lock chamber 10.

As explained in the foregoing, the ion beam etching method in accordance with this embodiment includes the cooling step S52, and thus can restrain the extraction electrode E from being deformed by heat. Specifically, even when the temperature of the extraction electrode E rises at the warming-up step S50, for example, the temperature of the extraction electrode E can be lowered by carrying out the cooling step S52. Therefore, thermal deformation can be suppressed in the extraction electrode E.

Since the deformation of the extraction electrode E is alleviated beforehand at the cooling step S52, the ion beam IB can be extracted at the etching step S54 after the cooling step S52 by using the extraction electrode E having alleviated its deformation. This can homogenize the radial distribution of ion beam intensity at the etching step S54 and improve the extraction efficiency of the ion beam IB.

FIG. 6 is a graph schematically showing the relationship between the value of RF power supplied from the power supply 48 to the coil 44 and time. As shown in the graph, etching is started at time t₁ and stopped at time t₂. In this case, the temperature of the extraction electrode E rises during time t₁ to time t₂. Since the extraction efficiency of the ion beam IB tends to decrease when the temperature of the extraction electrode E rises, it is necessary to increase the value of RF power in order to maintain the extraction efficiency. The ion beam etching method in accordance with this embodiment turns OFF the RF power during time t₂ to time t₃, so as to cool the extraction electrode E. This alleviates the thermal deformation of the extraction electrode E.

Thereafter, the next etching is started at time t₃ and stopped at time t₄. Since the extraction electrode E is cooled during time t₂ to time t₃ here, thermal deformation is suppressed in the extraction electrode E at time t₃. Therefore, the same RF power as that during time t₁ to time t₂ can also be applied during t₃ to time t₄. Consequently, cooling the extraction electrode E during time t₂ to time t₃ can restrain the value of RF power from fluctuating with time. Hence, etching can be effected with a high precision and favorable reproducibility.

Since the substrate W is conveyed at the cooling step S52, the substrate W is conveyed in parallel with the cooling of the extraction electrode E. This shortens the processing time of the whole process of the ion beam etching method. Preferably, the flow rate of Ar gas at step S11 is made greater than that at steps S4 and S17. This can efficiently cool the extraction electrode E. In particular, it will be preferred if the flow rate of Ar gas at step S11 is maximized.

The ion beam etching method in accordance with this embodiment is particularly effective when carrying out etching by a small depth, though it can also be used favorably when carrying out etching by a large depth. When processing the ABS of a thin-film magnetic head, for example, etching by a small depth is referred to as shallow etching, whereas etching by a large depth is referred to as cavity etching.

Though preferred embodiments of the present invention are explained in detail in the foregoing, the present invention is not limited to the above-mentioned embodiments.

For example, the cooling step S52 may be carried out after the etching step S54. In this case, even when the extraction electrode E is thermally deformed at the etching step S54, the deformation of the extraction electrode E is suppressed when the cooling step S52 is carried out.

The substrate W may be kept from being conveyed at the cooling step S52. The substrate W may be conveyed between the warming-up step S50 and cooling step S52, for example.

An inert gas different from the ion-generating gas for generating the plasma P within the discharge container 42 may be used as an inert gas for cooling the extraction electrode E. For example, He gas may be used for cooling the extraction electrode E, while using Ar gas as the ion-generating gas.

The present invention provides an ion beam etching method and an ion beam etching apparatus which can restrain the extraction electrode from being deformed by heat. 

1. An ion beam etching method comprising: an etching step of etching an object to be processed with an ion beam extracted by an extraction electrode; and a cooling step of cooling the extraction electrode with an inert gas.
 2. An ion beam etching method according to claim 1, wherein the object is conveyed in the cooling step.
 3. An ion beam etching method according to claim 1, wherein the cooling step is performed prior to the etching step; the ion beam etching method further comprising a warming-up step of extracting the ion beam by using the extraction electrode prior to the cooling step.
 4. An ion beam etching method according to claim 1, wherein the inert gas is identical to an ion-generating gas for generating an ion in the ion beam in the etching step.
 5. An ion beam etching method according to claim 4, wherein the inert gas has a flow rate greater than that of the ion-generating gas in the cooling step.
 6. An ion beam etching method according to claim 1, wherein the object is conveyed in the cooling step, and wherein the cooling step is performed prior to the etching step; the ion beam etching method further comprising a warming-up step of extracting the ion beam by using the extraction electrode prior to the cooling step.
 7. An ion beam etching apparatus comprising: an ion source; an extraction electrode for extracting an ion beam from the ion source; and a cooling device for cooling the extraction electrode. 